Panel board of the dead front convertible type



sepi. 25, 1934.

f H. J. L. FRANK 'I PANEL BOARD OF THE DEAD FRONT CONVERTIBLE TYPEoriginal Filed April 8. 1929 1o sheets-sheet 1 A TTORN st 'epL 25, 1934.Hf 1 L, FRANK 1,974,452

PANEL BOARD 0F THE DEAD FRONT CONVERTIBLE TYPE voriginal Filed April 8.1929 1o sheets-sheet 2 JNVENTOR.

A TTORNE Y.

Sept.' 25, 1934. H L. FRANK` 1,974,452V

.PANEL BOARD OF THE DEAD FRONT CONVERTIBLE TYPE original FiledApri1'8f1929 1o snets-sheet 3 INVENTOR.

E 2%;4 auf ff/1% j Sept. 25, 1934. H. 1 L FRANK ,974,452

PANEL BOARD 0F THE DEAD FRONT CONVERTIBLE TYPE Original Filed AprlrB,1929 lO Sheets-Sheet 4 A TTORNEY.

Sept. 25, 1934.

-H. J. L. FRANK PANEL BOARD 0F THE DEAD FRONT CONVERTIBLE T YPE Y 1osneetsfsheet 5 vori. .f,ina1 Filed April 8. 1929 S" linkin :a l

JNVENTOR. BY

Sept 275, 1934- H.. .1. L. FRANK f 1,974,452

PANEL BORDVOF THE DEAD FRONT CONVERTIBLE TYPE original Filed Abril 8,.1929 1o Sheets-sheet e INVENTOR.

ATTORNEY.

Sept. 25, 1934. H. J. l.. FRANK PAHL BOARD OF THE DEAD FRONT CONVERTIBLETYPE l0 Sheets-Sheet 7 Original Filed April 8, 1929 INVEVTOR.

sept. 25, 1934.. J, FRANK 1,974,452

PANEL BOARD 0F THE DEAD YFRONT CONVERTIBLE TYPE Original Filed April 8,1929 17.0 Sheets-Sheet 8 N Alul 11W/ENTOR-I ATTORNEY.

Sept. 25, l1934. H. J. 1..' FRANK PANEL BORD OF TH DEAD FRONTCONVERTIBLE TYPE Original Filed April 8, 1929 l0 Sheets-Sheet 9INVENToR.. BY j am f/V ATToRNE v Sept. 25, 1934; f H, J. l.. FRANK1,974,452

PANEL BOARD AOF' THE DEAD FRONT CONVERTIBLE TYPE originalV Filed April8. 1929Y 1o sheets-sheet 1o ATTORNEY Patented Sept. 25,1934

PANEL BOARD OF THE DEAD FRONT CONVERTIBLE TYPE Harrison J. L. Frank,Detroit, Mich., assignor to Bulldog Electric Products Company, Detroit,Mich., a, corporation of West Virginia.

.Application April 8, 1929, Serial No. 353,343 Renewed March 18, 1933 25Claims.

The invention of this application relates to electrical panelboards andparts thereof.

The principal object of the primary invention of this application is tosectionalize panelboards of the so-called feeder type, that is to say,one

wherein the circuits leading from the panelboard are of a large varietyof electrical capacities and characteristics, in such a manner that noextravagane of space is permitted.

Sectionalizing of panelboards has been satisfactorily accomplished inconnection with lighting distribution panelboards, these possessingtheenabling characteristic that the circuits leading therefrom aregenerally of similar capacity and nature. Because of this similarity,the problem of sectionalizing a lighting distribution 'panelboard is arelatively simple one.

However, for feeder panelboards, wherein the circuits are of widelydissimilar capacities and 20 characteristics and where an innite numberof combinations must be effected, sectionalizing is not so simple amatter.

While sectionalizing a panelboard of this type is not in itself adifficult matter, harmonizing the demands of sectionalizing with thedemands of space economy, and the demand of not having too many sizesand types of units, is a very difficult problem and until my solutionwas offered, there had been no satisfactory sectionalized panelboards ofthe feeder type.

It is observed at the present time that if the demands of space economyare to be ignored, sectionalizing of .feeder type panelboards could beeiected merely by cutting up a panelboard into a large number of units.This would provide large units and small units of various sizes and itwould be obvious that aunit large enough to receive large circuitelements would be quite wasteful of spacev if used to receive smallcircuit elements.

Further, because of the fact that a feeder panelboard mustaccommodate aninfinite variety of circuit capacities, circuitl characteristics, andcombinations, sectionalizing such a panelboard at rst appearedimpractical because of the fact that it was thought that an infinitevariety of units would have to be made and carried in stock to meetvarious conditions. Merely to indicate the variety of circuitcapacities, characteristics, etc., 50 there is presented here a tableshowing the various demands made upon feeder panelboards: 1.Poles-circuits may be of 1, 2, 3, 4, or 5 Y poles; l

2. Amperage capacities-circuits may be of 30,

. 60, 100,200, 400, 600, 800, 1200 Amp. etc.;

3. Voltages-circuits may be of 125, 250, 440, 575, or 660 volts;

4. Bus bar connectionscircuits may be connected in any of the followingways:

4 4 wire; 3-3 wire; 2 2 Wire; 3 qb to single rp; 60 2 p to single qb; 2p 3-wire to 2 p 4-wire and to 2 qs 5-wire; 3-wire 110-220 volt singleqs; the same with branches of 110 volt 2-wire -220 volt Z-Wire; 110-220volt 3-wire, etc.

These merely exemplify the numerous demands 66 that must be satisfied,by feeder panelboards.

A solution of the problem of sectionalizing feeder panelboards,consistent with the demands of space economy, and the demands ofmanufacturing economies, insofar as the variety of units 70 to becarried is required, etc., is the principal object of the primaryinvention of this application.

A key .to my solution may be found in my discovery that the advantagesdesired may be gained by proportoning the divisions of the panelboard sothat the dimensions of a panel builtgup of these divisions will beintegral multiples of the greatestcommon factors of the correspondingdimensions of the divisions Without, at the same time, necessarily beingintegral multiples of the corresponding dimensions of the divisionsthemselves. In other words if the length dimension is considered by wayof example, a dimension characteristic that is intimately associatedwith the result that an economy of space is effected will 35 be found tobe this; the length of a panel Will be an integral multiple of thegreatest common factor of the lengths of the divisions, and yet may notbe an integral multiple of the lengths of divisions. That is to say, Iestablish a der. relation between the length of the panel andthegreatest common factor of the lengths of the divisions, but no suchrelation necessarily exists between the length of the panel and thelengths of the divisions; the relation established is to the factor andnot to the division lengths.

In illustrating my invention, I have chosen, from a large variety, ofunits, units of the A, B, C, C1, and D type, combined to form SA, SB,SBi, SBz, SC, SCi, and SD circuit protecting divisions, and these havebeen chosen only by way of illustration of the many possibilities whichmy invention possesses.

Further, I have chosen to illustrate, as my units, units of the plug andreceptacle type, or of the movable head and xed base type, and this typeis chosen only by way of illustration.

Further objects of the invention are to provide novel details ofconstruction of circuit protecting m0 units, combined incircuit-protecting-divisions to form a. sectionalized panelboard.

Other objects of the invention will presently appear upon reference tothe following detailed description of a panelboard built in accordancewith my invention and of units useful in forming the panelboard of myinvention, the panelboard and these units being shown in the appendeddrawings in which Fig. 1 is a vertical longitudinal section of an Aunit, on lines 1-1 of Figs. 4 and 30;

Fig. 2 is a plan view of an A unit receptacle part; y

lill

Fig. 3 is a perspective view of an A unit plug part;

Fig. 4 is a vertical section on line 4.-4 of Fig. 1;

Fig. 5 is a plan view of what may be designated an A unit fuse limitingplate;

Figs. 6 and 7 are perspective views 'of two forms 0f A unit plug contactand fuse prongs, Fig. 6 showing a cartridge fuse in place in one of theprongs; Fig. 8 is a diagrammatic plan view showing a group of three Aunits with the plugs thereof ganged, as they may well be, to form a 3pole switch;

Fig. 9 is a perspective view of an A unit, whose plug is formed topermit of the insertion of a testing or other instrument into thecircuit line;

Fig. 10 is a longitudinal vertical section of the unit of Fig. 9;

Fig. 11 is a perspectivevview of a detail thereof;

Figs. 12 and 13 are partial sectional views showing the operation ofthis portion of the device;

Figs. 14 to 18 represent diagrammatically differentarrangements of themeans used with A units for preventing use of improper fuses in them.

Fig. 19 is a longitudinal vertical section through the receptacle partof a B unit, as if on line l1er-19, rig. 3o;

z Fig. 20 is a side elevation of a B unit plug;

Fig. 21 is a perspective view of a detail of construction thereof;

Fig. 22 is a side elevation of a B unit, with one of the plugs incircuit breaking relation, and

the other in circuit making relation;

Fig. 23 is a top plan view ofFig. 22; y Fig. 24 is an inside View of a Bunit, rec-eptacle with the bottom guard member removed;

' diagrammatically indicated in Figs. 31 and 32.

will-be dened: A panelboard includes a panelf l and the associatedmounting plate, box, etc. A' panel includes a number of circuitprotecting divisions grouped in an ordered appearance fashion; the termpanel may embrace all of the units in any one distributing center, or itmay embrace less than all of the units in any one distribution center.

A "circuit-protecting-division includes a desired vgrouping of"circuit-protecting-elements, (fuses, switches, etc.,) capable ofadequately protecting acomplete circuit, and associated with mountingand assembling body parts of insulating material, both the elements andtheir associated body partsbeing included in the word division. A unitis an article of manufacture including insulation blocks and circuitprotecting elements, and may comprise a portion of a block of insulatingmaterial, as in the case of the D units. or one or more blocks ofinsulating material, (as in the ca'se of two A units combined) orportions of one or more blocks of insulating 'as a block,

Capacity is the maximum load carrying ability, in amperes, of the partunder consideration. The capacity of a unit is its maximum load-carryingability, in amperes. The capacity of a panel is equal to the sum, inamperes, of j the capacities of the. units comprising the panel.

From Fig. 31, it will be seen that the divisions shown are of assortedwidths, across the bus bars, and assorted lengths along the bus bars,this beingl due principally t the different dimensions of the elementsthereof. For example, where the elements are in the nature of lowvoltage fuses, the divisions are generally narrow, and where theelements are in the nature of high voltage fuses, the divisions arewide. Also, divisions of the 2 pole type are comparatively shorter thansimilar divisions of the 3 p'ole type.

It might be well to mention at this time that thev dimensional size of afuse varies with its capacity. For example, a 60 Amp. fuse is larger incross section than a 30 Amp. fuse and smaller than a 100 Amp. fuse, etc.Because of this, a division which can accommodate fuses up to 200 Amp.size, cannot accommodate a 400 Amp. fuse, etc., but a division which canaccommodate a 400 Amp. fuse can also receive a smaller capacity fuse,provided it be equipped with fuse receiving means of the proper size,spacing, and type. The assortment of divisions shown diagrammatically inFigs. 31 and 32 will be briefly described.

The divisionreferenced SA in my design is l 11.,wide and 4X(5) long. Thedivision referenced SD, is 11" wide and 4X(5) long. The divisionsreferenced SC are each 51/2 wide and 3X(3%-"-) long. The divisionsreferenced SCi are each 5%" wide, and 3X(3%) long. The divisionsreferenced SB are each 51/2" wide and 6X(71/2") long. The divisionreferenced SB1 is 11'. wide and 2X(21/2") long. The

divisions referenced SBz" are each 5%" wide and 4X(5") long.

A characteristic of each division is its compactness, each' beingsubstantially as compact as possible, consistent with the requirementsthat the elements thereof be properly insulated, support-l ed, grouped,etc., and consistent with manufacturing tolerances.

For convenience of manufacturing, the divisions can be built up ofunits,.and a representative selection ofunits for the divisions of Figs.31-32 is shown in Fig.- 30 by way of example.

The SA division-may be made up of two A units, 11" x 2X each. The SDdivision may be made up of one D unit, 11" x 4X. The SC divisionstogether may be made up of one C unit, 11" x 3X, double branch type.''Ihe SCi divisions together may be made up of one C1 unit, 1l x- 3X,double branch type. The SB divisions may together be made up of three Bunits, 11 x 2X, double branch type.

each of the double branch type.

Other examples may be mentioned but are here omitted for purposes ofbrevity.

Each of the panels shown, therefore, includes.

the following units, all 11" wide; 2-A units, S-B units, l-C unit, 1-C1unit; 1-D unit; or eight units in all, forming eight divisions, Fig. 31,or nine divisions, Fig. 32.

The units, together form a panel, which is enclosed in a cabinet whosegutter plates cover the side edges of the panel formed of the units, andbecause of this, to preserve an. ordered appearance it is not necessarythat the units be all exactly 11" wide. Some may be lOl/2 wide and some11%, for example, without disturbing the ordered appearance of theboard.

Further, mounting means (not shown in Figs. 30-31) are provided andthese also may be spaced at uniform distances X.

It will be observed at this time that the mounting and connectionspacingX is only a fraction of the length of the shortest unit, beingone-half of the A and B length, and is accordingly a fraction of thelength of the shortest division.

Further, certain of the unit lengths are frac-gv tional multiples ofother unit lengths, C:B, CzA, for example, due to the fact that theunits and divisions are designed to be as compact as possible,notwithstanding the fact that some of the unit lengths arenon-fractional multiples of other unit lengths.'Y I can eiectinterchange of divisions and of units, without leaving gaps betweendivisions and-units, this being due to the fact that the mounting andconnection spacing X is less than the unit length, and that each unitlength is a non-fractional multiple of X.

Further, byvirtue of the fact that the dimensional characteristics orareas of circuit protective elements are substantially proportional rtotheir electrical characteristics or capacities, it will be seen that theareas of divisions, compacted to such elements, will prove to besimilarly proportional to their capacities. having a certain arrangementof divisions, and consequently a certain area, will have a ycertaincapacity and will always accommodate enough units to total substantiallythat capacity. This insures against overloading' of the feeders of apanel already installed, by rearrangement of units, and also permitsutilization of the feeders, and the panel area to practically capacity,regardless of what rearrangements of divisions take place. This feature,together with Thus, a panel other features of design, permitsreplacement of one arrangement or group of divisions by different ones,without there being any danger of disturbing the ordered appearance ofthe panel, without creating odd-size gaps in the pane1,with outoverloading the panel feeders, and without sacrifice of compactness ofthe panel as a whole.

Further, the divisions are subdivided into units, and these arecombinable in various ways to form different types of divisions. Forexam- `ple, a 7X division may be made of two 2X units plus one 3X unit,or of a 4X unit plus a 3X unit or of a 2X unit plus a 5X unit, etc. Or,a batch of 2X, 3X, etc., units may be grouped at one time to form 7Xdivisions, at another time 5X divisions, etc. Thus, where two'circuitswhose divisions have a total length of let us say, 12X are to bereplaced by five circuits totalling the same ca-.

pacity and also totalling 12X in length,lthe replacement can readily beeffected without gaps, as will be illustrated by considering the fivecircuit divisions, 12X in length, being made up of three 2X units anddivisions and two 3X units and divisions.

The method of laying out a sectionalzed panelboard system In order todesign a manufacturing system for sectionalized panelboards, wherein allof the demands of sectionalizing are adequately and satisfactorilycarried out, while retaining a satisfactory compactness for thepanelboard, I adopted a novel method of laying out my system and I nowdescribe it, since it aids in a complete understanding of my invention,although I do not now claim this method in this application.

I. First, I determined what complete-circuitprotecting divisions wouldhave to be provided by my system. In doing this, I created the desiredgroupings of the circuit-protecting-elements, listing all of thesedesired groupings. For example, I discovered that among the groupingswould be the following: 3-30 Amp. 250 V. fuses; 2-30 Amp. 250 V. fuses;3-100 Amp.'600 V. fuses, etc.

II. E then proceeded to arrange the individual elements of each group onbody parts of insulating material, to form divisions, in such a Way thateach division would be as compact as possible, consistent withtheelectrical and mechanical demands of insulation, strength, spacing, etc.and manufacturing tolerances. I discovered that in general, thedivisions could be divided into two widths; about 51A",-and about 11,respectively. I therefore, determined to observe the following rule asregards the widths of any divisions I might` design. I maintained forthe widths of the divisions, dimensions equal to integral-mul'tiples ofa common factor width, and s of lengths of divisions, the lengthsvarying fromv about 21/2 up to about 'l1/2, with intermediate lengths,at about 3%, 5", 6%, etc.

IV. I then determined for that assortment of lengths a proximate commonfactor, which proved to be in my design, 1%", I, therefore,4

redesigned my divisions so that their lengths would be integralmultiples of the common factor length. The lengths were found to be asfollows: 21A?, 3%, 5, 61A, 'l1/2, etc.

V. For conveniencefof manufacture, and also in order to reduce thenumber of lengths from e.- the ve mentioned to three, I subdivided thedivi- -mons into units, In certain cases, areas, were so subdivided thata number of units would form a complete division (SA) In another case,a, number of units formed a number of divisions (SB). In still anothercase, one'unit formed two divisions (SC-SC1). In another case, one unitformed one division (SD).

VI. I then proceeded to provide means for conl=- .r the elements of thedivision to the bus bars and means for mounting the units on the xedstructure, usually the mounting plate. I provided threaded holes in thebus bars to receive connection screws and also provided on y themounting plate threaded holes to receive mounting screws. I spaced thethreaded holes of the bus bars and of the mounting plate on uniformspacngs equal to the common Afactor length 1%". I did this inappreciation ofthe fact that my 1 of divisions (and of units) varied,not as integral multiples of the length of the shortest division (orunit), but as integral multiples of the common factor length, and Iappreciated that if the uniform spacing was chosen, not with relation tothe length of the shortest division,

but with relation to the common factor length, I could accommodate,1-with complete interchangeability, the intermediate lengths ofdivisions, that is those lengths which were not integral multiples ofthe length of the shortest division. A characteristic of vmy lay out,therefore,

.is the following relation, shown in Fig. 30.

. tolemes.

A still further relation is this: The overall length of the panel is anintegral multiple of the greatest common factor of the unit lengths, andyet it is not neeesarily an integral multiple of any unit length. Forexample, a complete panel could be built up of 2A units, 1D unit, 1Cunit,

and 3B units, in which case the panel length would be 17X. This would bean integral multiple of X (the `factor) but would not be an integralmultiple of 2X (the length of the shortest unit). The same applies to apanel including all but the C unit of the panel of Fig. 30.

As an ple of the space emciency of my design, wherein 'the abovementioned relation is a characteristic, I contrast the lay out disclosedin Figures 36 and 31 with a similar capacity lay out, wherein theuniform spacing is equal to (2X) the length of the shortest division orunit, rather than. as on my design, where the uniform spacing X isone-half of the length of the shortest unit. From Figs. 30 and 31,itwill beseen that the length of the'panelboard shown is 20X or 25".Now,`i the spacing had been (2X). equal to the length of the shortestunit, I would nothave'been able to provide C or C1 units of the 3Xlength, but would have had to provide for these.

lengths of 4X. Accordingly, my SC, and SCi sections would be "4X longrather than. 3X

V long.i Altogether, the panel would be' 22X or 2711' long. By mydesign, therefore, I save 2X or 2541' on the p'anel shown whichis asaving of 'one channel.

about 10%, all due to the fact that my divisions are compact and theuniform spacing X is a fraction of the length of the shortest sectionand unit.

Greater savings in length result where the number of 3X and 5X sectionsis comparatively great.

Now having described a representative panelboard, and my layout method,l'. describe in detail two only of the units I provide, these beingchosen by way of example.

In Figs. 1-5 I show an A unit; in Figs. 9-13, I also show an A unit,having a testing plug, and in Figs. 19-29, I show a B unit.

The "A unit The A unit shown in Figs. 1-5 is a plug and `receptacle typeswitch having a fuse therein to has a connecting opening 25 leadingoutof the end of the receptacle. V

The oor of the receptacle covers the central channel and part of theside channels and shields the interior of the receptaclefrom the bus barspace, and is provided with a 'low cross-rib or barrier 26 immediatelyover one of the intermediate legs 21.

ceptacle. Each of these openings (23 and 24) Secured to the oor of thereceptacle 20 as by screws 27 and extending from barrier 26 to the endwall beyond opening 2e and preferably bent so as to lie below opening 25is a conducting plate or bar 28 carrying at its outer end a pair ofiixed or receptacle contact iingers 29 which extend well up above thereceptacle iioor but whose upper ends are considerably below the top ofthe walls thereof and below the inwardly projecting .shielding portions30.

At the other end of the receptacle floor is a second bar or plate 28a,similar to plate 28, except that it is not so long, as, it overlies onlyAlso within receptacre 20 and secured to barrier 26 as by screw 3lpassing through hole 31a thereof is a strip of insulating material 32,shown. in plan in Fig. 5. This strip 32 may be designated the fuselimiting strip and is provided with a plurality of pairs of screw holes,care.- fully located, through which preventive forks or limiting membersor stops 33 may be selectively attached thereto. 'These stops are shownin Fig. I as secured in holes numbered 3 and 5, Fig. 5.

The plug part 50 of the unit is of insulating material shaped to twithin the upper portion of the receptacle and-is provided with asuitable hand grip 51' on its outer face, which may consist of a metal.plate tooshort to extend from one pair of iingers' 29 to the other sothat when the' block 50 is inserted top down there can be no currentiiow and all live parts are hidden. The edges of the plug are cut awayfrom the edges of the plate as shown, to provide linger grip cavities51a, Fig. 3.

The under side of plug 50 carries at each end plug contact and fuseprongs, which, for the 30 Amp. 250 V. fuse shownin Fig. l, comprise plugcontacts 52, attached to plates 53 secured 150 any A unit receptacle 20,so as to be completely interchangeable with non-testing A unit plugs.

At one of its ends, the testing plug may be similar to any non-testing Aunit plug 50. At its other end however, the testing plug 50T is providedwith a large cavity opening to the under face of the plug and having asmall opening 76 to the upper face. 'I'he conducting plate 53aT to whichthe fuse 58 is attached at the end containing the cavity 75 does notextend to the end of the plug 50T but projects beyond the edge of thecavity only for a short distance. The plug contact 52T, adapted to coactwith a contact 29 in the receptacle 20,'is formed on a small plate 53bTsecured to the plug as by screws 5401, which plate 53bT, has a verticalextension 77 extending up into cavity 75 at one end thereof, nearopening 76.

Plate 53aT and the parts connected directly therewith are shown more indetail in Figs. 11, 12, and 13. To one end of plate 53aT is xed anL-shaped spring abutment 78 and back of this, one end of a exible lead79. To the other end of lead 79 is ixed a small plate 80 provided withcurved ends 81 as shown. Fixed to the end of lead 79 adjacent plate 80,is one end of a coil spring 82, whose other end is xed to the uprightportion of the L-shaped abutment 78. Lead 79 and the spring 82 are ofsuch construction as to allow the plate to be pressed firmly againstpart 77 of plate 53bT.

The electric connection in this form of plug,'

from. the contact 29 in one end of member 20 to the contact 29 in theother end thereof is through contact 52T to part 77, to plate 80,through lead 79 to plate 53aT, then through the fuse 58, to plate 53 andthe other contact 29.

By means of this form of block and the form of bipolar instrumentterminal shown in Figs. 9, 12, and 13, an instrument may be connected tothe circuit line in series or disconnected therefrom without opening thecircuit line or interrupting current flow therethrough.

The form of terminal shown consists of two plates of conducting materialconnected to the two poles of the instrument, d secured on oppositesides of a thin strip of insulating material 101 which may project ashort distance beyond the ends of the plates.

When the tip of this device is inserted in opening 76 it easilyseparates the upper end of plate 80 from part 77, while the spring 82holds the lower end of plate 80 in contact with part v77 until plates100 have contacted with parts 77 and 80 respectively, thus maintainingthe one circuit until the other is also completed. The reverse operationoccurs upon withdrawal of the terminal, the circuit through theinstrument being maintained until the parts 77 and 80 are once more incontact and the main circuit is completed.

An A unit plug is adapted to be used with any A unit receptacle to forma switch. Placing the plug in the receptacle with the fuse outwardbreaks the circuit and indicates that the circuit is broken, and placingit in the receptacle, with the fuse inside, completes the circuit, andindicates that fact.

It should be noted that the plug of Figs. 1-5 is identical in shape andouter dimensions with the plug shown in Figs. 9 to 11 andinterchangeable therewith so that one may be substituted for the otherwithout change and tests carried out when desired without interruptionof service.

It will be observed that while parts 20 and 50 are named as receptacleand plug, they might well be termed base and head, etc.

The B unit This unit, shown in Figs. 19-29, includes two integrallyformed receptacles,` and two separate plugs therefor, each receptacleand its plug forining half of a B unit. The unit is of the samedimensions as the A unit and is interchangeable therewith, as can bereadily seen.

The B unit includes a cup shaped part 120 formed of suitable insulatingmaterial, and including end legs 121 and intermediate legs 122, thelatter containing suitable bores 123 through which -may be passed boltsfor securing the part 120 to a suitable supporting base, not shown.

The bottom of the cup shaped part is provided with three suitably spacedknockouts 124 providing means through which connection may be madebetween the elements inside the part and the bus bars 125, which latterare mounted in any suitable fashion on the supporting base, between legs121 and 122, as indicated. In the drawings, one of the knockouts isremoved, and a screw 56 and bushing 56a are shown as replacing thatknockout.

Inside of the part 120 and at its ends, suitable terminal connectingplates 126 are mounted and to' these may be bolted lead terminals, 127.These y tacle contacts 128 lying close to the said wall and under anoverhanging insulating portion 130 formed thereon. The exposed halves ofthe contactsv 128 are provided with protecting cover pieces 131 ofinsulating material. The provision o f parts 130-130 protect thenormally live contacts 128 against accidental touching when .thereceptacles are open.

In the central portion, the part 120 is provided with a metallic plate135 overlying the central knockout and one of the others whereby thisplate may be connected to anyone of the three bus bars over which thereceptacle is to be placed. This plate 135 is provided with two sets ofreceptacle contacts 128a located on opposite sides of the cross centerline of the part 120 and on opposite sides of the longitudinal centerline thereof, so that, when the part 120 is divided into two receptaclecompartments by means to be described, each will have receptaclecontacts in diagonally opposite corners.

With the plates 126 and 135 in position, the part 120 is divided intotwo receptacles or compartments by a removable insulating wall or shield140 slidable in guides 141 provided for this purpose. The wall 140preferably carries also a cover piece 142 of insulating material whichoverlies the plates 126 and 135 so that when this wall unit, which isshown in Fig. 26, is in position, all of the live parts are guardedagainst accidental touching.

One of the two plugs 150 is shown in detail in Figs. 20, 21, 27, and 28as consisting of a portion of insulating material of such size as to tand ll one of the receptacles and a suitable bail 151, therefor, isprovided to aid in withdrawing the plug.

The side of the plug opposite the bail 151, is provided with dependingside walls 152 which aid in piloting the plug into proper position forengagement of the plug contacts 153 carried thereby with the receptaclecontacts 128, 128er. These plug contacts 153 are mounted at diagonallyop- Levanta to the plug as by screws 54 passing through the block andhaving their heads sunk well below the upper surface, out of contactwith 'hand plate 51. Plates l53 extend from near the central portion ofthe plug to close to the ends thereof and have the contacts 52 at theirouter ends where they are in position to mate with contacts 29 of thereceptacle. To their inner ends are attached fuse clips 55 for thereception of the 30 Amp. 250 V. fuses 58 for which the device isadapted. It will be observed that eachstructure 52-53-55 is consideredas a plug contact and fuse prong.

With a bus bar 125 electrically connected to plate 28 by a screw 56 anda bushing 56a, extending through the center hole 56h in the i'loor ofthe receptacle 20 and into the bus bar hole H, as shown clearly in Fig.1, replacing the knockout that had been in hole 56h. and with a loadcable 57 secured to plate 28a by screw 57a as shown in the same gure,the connection through the fuse 58 from bar 125, to cable 57 'is made byinserting the plug 50 into the receptacle, with contacts 52 engagingcontacts 29.

Fig. l shows the plate 28 connected through center hole 56h to thecenter bus bar 125,and cable 57 connected to plate 28a. If the plate 28is' to be connected to the bus bar in the right hand channel, foradiierently phased`connection,-screw 56 and bushing 56a are placedthrough the right hand connection hole 56e, the knockou 56d at thatpoint being removed, just as the center knockout had.been for theconnection shown. If the plate is to be connected to the bus bar in theleft hand channel, the unit as a whole is reversed 180, and the screw56, passed through the hole 56o, will align with the left hand bus.

It will be observed that the two holes 56h and 56e through which screw56 and bushing 56a may pass and which open the interior of thereceptacle to the bus bar channels are normally closed, one being closedby the unremoved knockout, and the other by the bushing and screw, andthis is normally true regardless of which bus bar is connected to strap28. The knockouts, therefore close the bus bar compartments in back ofthe units. To complete the closure of the receptacle floor, aninsulation sheet 56e is secured to the receptacle iioor at opening 23.

Fuse limiting The plifgs of various A units are constructed so as to beinterchangeable, and for this reason I provide means for preventing theplugging-in of an A unit plug having a fuse of higher amperage or lowervoltage into an A unit receptacle which should not receive such a fusedplug and such means will now be described.

In general such means includes preventive forks 33 so mounted in thereceptacle as to prevent insertion of a plug having an improper fuse.The forks are adjustable and removable and are used according to theschedule shown in Fig. 5.

The unit shown in Figs. '1 4 happens to be' arranged for the receptionof a 30 Amp. 250 V. fuse, which is the smallest dimensionedsize fuse forwhich the unit lis adapted. As so arranged, the fuse ends are-receivedin clips 55 and the forks are positioned in holes 3 and 5 (Fig. 5) thisspacing permitting the insertion oi' an"A unit plug having a 30 Amp. 250V. use.

If' a plug is equipped with a 60 Amp.'250 V. fuse, the fuse ends will be.received in clips 55a (Figs. 14-15), which are so positioned on theirprongs that they will be to one side of the longitudinal center line ofthe unit, and so that -they would engage the forks 33 if the latter wereset in holes 3 and 5 for a 30 Amp. 250 V. fuse. A receptacle whose forksare spaced for a 30 Amp. 250 V. fuse could not therefore receive a 60Amp. 250 V. fuse or any larger dimensioned size fuse. To permit thereceptacle to receive a 60 Amp. 250 V. fuse, the receptacle forks wouldhave to be placed in holes 2 and 6, as indicated.

If a plug is equipped with a Amp. 250 V. fuse (Fig. 18), the fuse ends,formed as blades, would be positioned'in the parallel blade clips 52e(Fig. 7) formed on a plate 52h having a plug 'contact 52d and a tongue52o, the prong structure 52h, 52e, 52d, 52e, replacing the structure`52, 54, 55, of Figs. 1-4. If a plug so equipped were inserted into areceptacle intended to receive plugs having fuses of lower amperage, theforks 38 of that receptacle would engage parts of the structure 52h-52e,preventing complete insertion. To permit the receptacle to receive alOOAmp. 250 V. fuse, the forks would have to be set in holes 1-7 of plate32, Fig. 5.

If a plug is equipped with a 200 Amp. 250 V.

fuse, referenced 60, (Figs. 6 and 16) the fuse ends 61, formed asblades, would be positioned in the parallel blade clips 62 formed onplate 52a. 'the latter having a plug contact 63, a tongue 62o, and afuse holding screw 62a, structure 52a, etc., replacing the structure52-55 of Figs. 1-4. If a plug so equipped were inserted into areceptacle intended to receive plugs having fuses of lower amperage, theforks 33 of that receptacle would engage parts of the structure 52a,etc., preventing complete insertion. To permit the receptacle to receivea 200 Amp. 250 V. fuse, the forks would be omitted entirely.

If a receptacle is equipped to receive a 30 Amp. 600 V. fuse (Fig. 17)the insertion of a plug having a 60 Amp. 250 V. fuse cannot be effectedsince the clip 55a of that plug would be engaged by the fork 33 of thereceptacle.

From these examples it may be seen that the parts may be so arranged asto prevent the insertion of a plug 50 carrying a standard fuse ofeitherhigher amperage value or lower voltage value than that for whichthe parts are set.

Gangz'ng Fig. 8 shows the possibility of grouping three A units over acommon three bar arrangement to form a 3 pole SA division, similar tothe 2 pole SA division of Fig. 31. It shows for example, the three Aunits connected to the three bus bars 125 selectively, with one of theunits reversed 180 in position. 'I'he plugs of the three units areganged to form a, 3 p'ole switch, by a plate 250, connecting the threeplugs,` and connected to each of them by screws 251. This plate is soconnected to the plugs by the screws that the plugs can move slightly onthe plate,

4relatively to one another, to compensate for'diiculties in plugging in,and thus facilitating insertion or plugging in of the 3 pole switch.

It will be understood that the ganging principle may be applied to anydivision, and for example, two or more B unit plugs may be .ganged, ifdesired.

' its posite corners of the plugs, each being one branch of an L-shapedplate 154 secured to the plug at one end. These plates 154 are providedwith suitable tapped openings by means of which fuse holding clips'orngers 155 are bolted thereto. The tapped openings referred to areseveral in number and so located that several sizes of fuses may beprovided for. The form shown in Figs. 20 and 27 for example, is for afuse having a round end, while that in Fig. 28 is for a cartridge fusehaving a blade end.

As it is intended that a plug carrying a fuse 156 may be placed in itscompartment in reversed position when it is desired to maintain thecircuit broken, means are provided to hold the `plug 150 securely insuch position. This means may consist of a small plate 160 bent over oneedge of the plug and having the bent over edge cut nearly across so asto providea tongue 161 having a teat 162 adapted to coact with the sidewall of the receptacle 120 when the plug is reversed, and inserted.

Further, in order to provide means for testing the fuses withoutremoving plugs 150, .openings 165 (Fig. 23) are provided through theplugs 150 from their outer to their inner faces, within the area coveredby plates 154. These openings permit the insertion of contact wires orrods connected with any suitable indicator (not shown).

A means to prevent exchange of the plugs of two or more"B units isindicated in Fig. 23, in which gurethe plugs are shown as provided withslots 175 cooperating with screws 176 projecting through side walls ofthe receptacles. It is of course obvious that other plugs, not soslotted, could not be inserted, in such receptacleswhen the screws arein position. Other forms of projections and slots may of course be usedYto accomplish a like purpose. Y

.This case is in part a continuation of applicaton, Serial No. 175,173,led March 14, 1927, on Electric fusing devices.

Summary From the foregoing, it will be seen that there has been provideda sectionalized panelboard whose units may be provided with `means toprevent the combining with any unit of a fuse larger than the oneintended to be used with that particular unit, the means beingadjustable and removable so that the fuse receiving characteristics ofthe units may be varied as desired.

It will further be seen that there has been provided a sectionalizedpanelboard-having units on to which circuit protective elements, such asfuses, may be assembled and connected into or disconnected from thecircuits, without danger to the operator; that is, insertion or removalof fuses into their clips can be accomplished only when the circuitsthrough the fuses are dead. Further, the units are so constructed thatfuse replacement can be effected only when the operator is remote fromthe live parts of the panelboard, or is completely shielded therefrom byinsulation.

Further, the panelboard is so constructed that units may be readilyconverted to and from testlng'type from and to non-testing type, andwhen of the testing type, circuit testing may be carried on withoutinterrupting or disconnecting the tested circuit.

Further, it will be observed that each unit.

while adaptable for several sizes of circuit protectiveelementsY (fuses)is only slightly larger in dimension than the largest elementl (ruse)for which it is designed, this feature causing the units to be ascompact as efficiently possible.

Further, it will be observed that suitable barrier constructions betweenopposite polarity parts are provided, the barriers facilitating thecompacting of the units, by reducing the sizes'thereof. Further, it willbe observed that the panelboard is so constructed that all the desirableoperations such as changing of circuits, refusing, rephasing, installingunits, testing, etc., which require manipulating of the manipulablescrews, etc.,in the receptacle, maybe accomplished from the front sideof the panelboard.

It will further4 be observed that a wide range of convertibility isassured, even though a small assortment of units is provided, the unitsbeing combinable so as to create a great variety of divisions, as tosize, capacity, number of poles, etc.

It will'further be observed that since the panelboard is ofthesectionalized type, it possesses all of the advantages inherent tosectionalized panelboards, and that this is accomplished withoutsacrifice of compactness or convertibility, even though the circuitrequirements are of a wide range, as necessary for power distributioncontra-distinguished from lighting distribution. -Further, each unit isso constructed that the interior thereof is completely shielded from thelive or bus bar space in back of the unitf either by the knockouts whichhad not been removed or by the screw and bushing insertedlin aholewherein a knockout had been removed.

Further, a great degree of interchangeability is provided by the factthat A units are interchangeable with B units, etc., 'and parts of Aunits are interchangeable with parts of other A units, etc. Further, byvirtue of the fact that the units can be connected selectively to anybus bar, convertibility is assured.

Further, the provision of the insulating plates adjacent the oor of thereceptacles, combined with the overhanging portions of the receptaclewalls and other insulating pieces, completely shields the live parts ofthe receptacles.

, Further, the various types of vunits have interchangeable, andstandardized/mounting and connection details, which enhances the interichangeability and convertibility of the panelboard.

Further, by virtue of the specific type of connection and mounting meansprovided, interchange of units is facilitated, and may be accomplishedfrom the front of the. panelboard, this also applying to rephasing lofthe units, that is to say, `disconnecting them from the bus bars towhich they had been connected and connecting them to diierent bus bars.Further, working on units, without disturbing other units, or thecircuits therethrough, is readily possible.

vNow having described preferred .embodiments of my invention, referencewill be had to the following claims for a determination of the scope ofmy invention.

'I claim:

l. In a panelboard of the class describeda plurality of spaced bus barsand a plurality of vclosely adjacent circuit protective units mounted infront of and over and connected to said bus bars, each unit having aplurality of depressions on the back thereof spaced in a mannercorrespondng to the spacing of said bus bars so that when a unit isplaced over said bus bars, each depression will align with abus bar toform a compartment for each bus bar, and av knockout" in each depressionintegral with said unit', whereby any desired one ofthe knockouts may beremoved to expose any desired one or more of the bus bars to the frontof the unit, the knockou when in place serving as an insulating shieldbetween a bus bar and the front side of the units, the knockoutsbeingaccessible from the front of the panelboard for removal.

2. In a panelboard of the class described, a plurality of bus bars; aplurality of contacts xedly mounted with respect to each of and spacedalong said bars, a plurality of heads having contacts adapted to engagethe xed contacts and means to mechanically connect two or more of saidheads to operate in unison whereby a fganged head may be formed, saidmeans being readily releasable from and attachable to said heads so thatthe latter may be operated independently or in unison interchangeably,said means when attached permitting a slight movement of a. headrelative to its neighbor to compensate for diiiiculties in interengagingcontacts,

front of and over said bus bars, a plurality of conducting partsdisposed within said receptacle, and a plurality of manipulable partsdisposed within said receptacle and selectively adapted to cooperatewith one another, and with the threaded apertures, for mounting andconnecting purposes, all of said parts being wholly manipulab from thefront of the panelboard.

4. In a panelboard of the 'class described, a plurality of bus bars,units comprising a plurality of similarly constructed bases iixedlyconnected to said bus bars, and a plurality of similarly constructedremovable heads, said heads being adapted toselectively andinterchangeably cooperate with said bases, and means attachable to anddetachable from said. units whereby undesirable interchange of heads andbases is prevented.

5. In a panelboard of the class described, three parallel, equallyspaced bus bars, and a plurality of bases over and in front of said busbars, each of said bases being provided with two holes therethrough forthe reception of members adapted to contact with two of the bus bars,the holes aligning with an end and a center bus bar, and a knockout ineach hole, the bases being symmetrical about the center bus bar.

6. In a panelboard of the class described, three parallel equally spacedbus'bars and a plurality of units over and in front thereof, each havingend and center contacts adapted to engage the end and center bus bars,the ends of each unit being identical in shape so that the unit may bereversed 180 to permit the end contact to engage the other end bus bar,without disturbing the ordered appearance of the unit in the panelboard.

7. In a panelboard of the class described, a plurality of bus bars,units having contacts exposed to the sides thereof nearest the bus bars,and sheets of insulating material removably secured to said units toform barriers between the bus bars and the contacts or to expose saidcontacts to the bus bars. v Y

8. In a panelboard of the class -demribed, a plurality of bus bars, aplurality of head receiving bases in front thereof, all havingsubstantially the same width and lengths equal to integral multiples ofa predetermined common :factor length, and all having identicalconnection details whereby they may be interchangeably connected to saidbus bars, certain of said bases being constructed to receive one widehead and certain being constructed to receive a plurality of narrower hds, said bases and said heads comprising in ually cooperating bodiesupon which vare dispsed mutually cooperating contacts, the

length, and all having identical connection details whereby they may beinterchangeably connected to said bus bars, certain of said bases beingconstructed to receive one wide head and certain being constructed toreceive a plurality of narrower heads, said bases and said headscomprising mutually cooperating bodies upon which are disposed mutuallycooperating contacts, similarly sized and shaped heads being relativelyinterchangeable, said bases being provided with means to prevent thecombining therewith of any but the head or heads which that base isintended to receive.-

l0. In a panelboard'of the class described, a plurality of closelyadjacent units having remov- '.ab1e heads, a plate connected to andextending across a plurality of said heads to form a multihead switchingunit, the heads being movable relatively and with respect to the plateto permit quick-switching action.

11. In a panelboard of the class described, a plurality of closelyadjacent plug and receptacle units, means for mechanically connectingtwo or more plugs to operate in unison as a ganged plug, said meansbeing readily releasable from or attachable to said plugs so that theymay operate independently or in unison, said'means when attachedpermitting a slight movement of a plug relative to its neighbor tocompensate for dimculties in plugging in, due to friction.

12. In a panelboard, of the class described, a plurality of bus bars, aplurality of cup shaped, plug receiving receptacles thereon, all havingsubstantially the samewidth and lengths equal to non-fractionalmultiples of a predetermined common factor length, and all havingidentical mounting details, whereby they may be interchangeably mountedon said bars, certain of said receptacles being constructed to receiveone wide plug, and certain being constructed to receive a plurality ofnarrower plugs, said plugs and said receptacles each comprising a bodyof insulating material upon which are disposed mutually cooperatingcontacts, the latter being inaccessible when the plugs and receptaclesare in cooperative changeably mounted on said bas, certain of saidreceptacles being constructed'to receive one wide plug, and certainbeingconstructed to receive a plurality of narrower plugs, said plugs andsaid receptacles each comprising a.l body of insulating material uponwhich are disposed mutually cooperating contacts, the latter beinginaccessible when the plugs and receptacles are in cooperavlilifunctioning members, means accessible from the tive relation, the plugscarrying fuses which are enclosed within the receptacles when the plugsare plugged in.

14. A sectionalized panelboard of the dead front convertible typeincluding a plurality of fixed bus bars, a plurality of `units havingbases iixedly mounted with respect to said bars and connected to one ormore of them by selective connectors, each unit being provided withcircuit protective velements and with a head carrying means to connectsaid elements, said heads being movably mounted with respect to saidbases so as to be movable to and from circuit connection posiinterchangeof heads, as well as adjustment of fuse receiving means in the units, ispermissible without disturbing the ordered appearance oi the panelboard,each unit being provided with removable means to prevent the receivingthereby of any but a fuse for which it is intended.

l5. .a sectionalized panelboard employing a plurality oi' adjacent unitswhich are relatively interchangeable without disturbing the orderedappearance of the panelboard as a whole, each unit being provided withadjustably mounted and replaceable means for receiving and holding acartridge fuse, so that different sizes and types of fuses on a unit maybe interchanged, cach unit including a xed base and a movable headcarrying the iuse receiving means, the heads of various units beinginterchangeable for fuse interchange, each base being provided withremovable means for preventing the mounting thereon of any but the head`for which it is intended.

16. A sectionalized panelboard including a plurality of bus bars, aplurality of units, each of which is provided with circuit protectiveelements including convertible and replaceable cartridge fuse receivingmeans, and each of which is further provided with relatively movableswitchfunctioning members, means accessible from the front of thepanelboard for connecting the units to one or more of the bus bars asdesired, before or after the panelboard is formed 4as a whole, the meansbeing so interlocked with respect to the switch-functioning members thatexposing themeans for connecting them to bus bars is not possible unlessand until the switch functioning members have been moved to the positionin which they break the circuit through the unit.

17. A sectionalized panelboard including a plurality of bus bars, aplurality of units, each-oi front ci the panelboard for connecting thelunits to one or more of the bus bars, as desired for phasing andrephasing, before or after the panelboard is formed as a whole, themeans being concealed by the switch functioning members, when they arein a circuit making position, so that exposing the means for are-phasing is not possible unless and until the switch-functioningmembers have been moved to the position in which they break thecircuit'through the unit, the cartridge fuse receiving means beingsimilarly interlocked with respect to the switch-functioning members.

18. A sectionalized panelboard including a plurality of bus bars, aplurality of units, each of which is provided with circuit protectiveelements including convertible and replaceable cartridge fuse receivingmeans, and each of which is further provided with relatively movableswitchfunctioning members, means accessible from the front ofthepanelboard for connecting the units to one or more of the bus bars,as desired, before or after the panelboard is formed as a whole, themeans being so interlocked with respect to the switch-functioningmembers that exposing the means for connection to bus bars is notpossible unless and until the switch-functioning members have been movedto the position in which they break the circuit through the unit, thecartridge fuse receiving means being similarly interloclred with respectto the switch functioning members, the units being interchangeablymounted on the panelboard, the construction as a whole being such thatinterchange of units, adjustment, interchange or replacement of fuses,and changes of phasing are all impossible of performance while there isa current through the unit considered.

i9. A vsectionalizedpanelboard including a plu- 'units mounted over andconnected to said bus bars, means for connecting the units to any one ormore of the bus bars, the units having lengths equal to integralmultiples of the spaces between said connection means, each of saidunits having therein adjustable and interchangeable cartridge fusereceiving means and having switch functioning members, the latter beingso mounted that access to the live parts of the. units is not possibleuntil and unless the switch functioning members have been moved to theircircuit interrupting positions.

20. A sectionalized panelboard including a plurality of bus bars havinguniformly spaced connection means, a plurality of circuit protectiveunits, mounted over and connected to said bus bars, means for connectingthe units to any one or more of the bus bars, the units having lengthsequal to integral multiples of the spaces between` -rality of bus barshaving uniformly spaced coni their circuit interrupting positions, allof the units being of the same width, so as to present an orderedappearance when combined to form a panelboard. I

21. A sectionalized panelboard including a plurality of bus bars havinguniformly spaced connection means, a plurality of circuit protectiveunits, mounted over and connected' to said bus bars, means foiconnectingthe units tc any one or more of the bus bars, the units having lengthsequal to integral multiples of the spaces between said connection means,whereby the units may be interchangeably mounted on said bus bars, eachof said units having therein adjustable and interchangeable cartridgefuse receiving means and having switch functioning members, the latterbeing so mounted that access to the live parts of the units is not`possible unless and until the switch functioning members have beenmoved to their circuit interrupting positions, the switch functioningmembers indicating at a. glance. by their position, the condition of thecircuit through them and the unit being considered, the connecting meansfor the units including parts to'which access for connection purposes,can be had from the front of the panelboard, the parts beinginterlocke'd with the switch members, so that access thereto forconnection can be had only when the circuit is interrupted. y

22. A sectionalized panelboard including a plurality of bus bars havinguniformly spaced connection means, a plurality of circuit protectiveunits, mounted over and connected to said bus bars, means for connectingthe units to any one or more of the bus bars, the units having lengthsequal to integral multiples oi the spaces between said connection means,whereby the units may be interchangeably mounted on said bus bars, saidunits having therein adjustable and interchangeable cartridge fusereceiving means and having switch functioning members, the latter beingso mounted that access to the live parts of the units is not possibleuntil and unless the switch .functioning members'have 'been moved totheir circuit interrupting positions, the switch functioning membersindicating at a glance, by their position, the condition of the circuitthrough them and the unit being considered, the switch functioningmembers including 'relatively movable switch parts having fuse receivingmeans and one of which covers the other part to enclose the fuse withinthe interior of the unit.

23. A relatively large area sectional panelboard including a pluralityof xdly mounted busbars having uniformly spaced connection means, a

means is prevented unless and until the current through said unit hasbeen interrupted, each of the units also having therein means forreceivlengths equai to integral multiples of the spaces between saidconnection means, phasing means selectively and interchangeablyconnecting said units to onelor more oi said busibars, said units beingalso provided with adjustable fusing means for holding and connectingany one of a number of different sizes and types of cartridge fuses,conti-oi means for the units, the construction as a whole being suchthat the phase and fuse characteristics of each circuit may be varied byinterchange of the units and/or of the controlv means thereof, therein,the said phasing and fusing means being interlocked with respect to thecontrol means in each of the units so that any changes in the phase andfuse characteristics of a unit cannot be made until the current throughthe unit has been interrupted.

25. A relatively large area sectional panelboard comprising a boardhaving a plurality of fixedly mounted bus bars having uniformly spacedconnection formations, a large number of relatively small area, closelyadjacent, interchangeable circuit protective fused, current lead-oirunits connected to said bus bars by connecting n@ means cooperating withsaid connection formations, said units having diierent lengths, equal tointegral `multiples of h; spaces between said connection formations, te'units being provided with relatively movable, switch-functioningmembers; interchange of the unitsbeing possible without disturbing theordered appearance of the panelboard as a whole, access to the means forconnecting the units to the bus bars being impossible unless and untilthe switch functioning members have been moved to the position in whichthey break `the circuit through the unit being considered.

HARRISON J. L. FRANK.'

